PROPERTIES OF SALTED YOLK SOLIDS AND THEIR FUNCTIONALITY IN MAYONNAISE 1

The apparent viscosity, emulsification capacity, and functionality in mayonnaise of plain, free-flow, and low viscosity yolk solids were studied. Liquid yolk was used for comparison. All three types of yolk solids had considerably higher apparent viscosities than liquid yolk and there was a siginficant (P > 0.05) difference in apparent viscosity between each yolk solids sample. Free-flow yolk solids had the highest apparent viscosity, followed by plain yolk solids and low viscosity yolk solids. There was no significant (P > 0.05) difference in emulsification capacity between plain and free-flow yolk solids. Low viscosity yolk solids had a significantly (P > 0.05) lower emulsification capacity. There was a significant (P > 0.05) difference in apparent viscosity mayonnaise made from each yolk solids sample. Mayonnaise made from liquid yolk had the highest apparent viscosity. Of the mayonnaise samples made from yolk solids, that made from low viscosity yolk solids had an apparent viscosity of 38,250 c.p.s., followed by plain yolk solids mayonnaise at 29,500 c.p.s. and free flow yolk solids mayonnaise at 23,000 c.p.s. Although mayonnaise made from liquid yolk had a slightly higher spread, there was no significant (P > 0.05) difference in spread among the mayonnaise samples made from the three types of yolk solids. Mayonnaise made from free flow yolk solids had the highest stability at 12 days. Mayonnaise samples made from plain and from low viscosity yolk solids had stabilities of 10 days.     

INFLUENCE OF FROZEN STORAGE TIME ON PROPERTIES OF SALTED YOLK AND ITS FUNCTIONALITY IN MAYONNAISE1

The effect of frozen storage time on apparent viscosity of yolk, emulsification capacity, and functionality of salted egg yolk in mayonnaise was studied. Apparent viscosity of yolk increased considerably after only 24 h of frozen stage. Apparent viscosity of yolk stored 30 days was approximately three times greater than that stored 24 h. Yolk stored 90 days had the highest apparent viscosity. Storage of yolk for even 24 h resulted in a reduction in emulsification capacity. Yolk stored 30 days had the lowest emulsification capacity at 5.92. Yolk stored 60 days had an emulsification capacity of 6.10, and that stored 90 days had an emulsification capacity of 6.06. Mayonnaise made from yolk stored 60 days had the highest apparent viscosity and the lowest spread. There was no significant (P > 0.05) difference in apparent viscosity and spread of mayonnaise made from yolk stored 0, 30, or 90 days. Mayonnaise made from yolk stored 24 h had a mean stability of 22 days. Subsequent frozen storage of yolk for 30, 60, and 90 days produced mayonnaise with mean stabilities of 21, 20, and 21 days, respectively.     

THE EFFECT OF HEAT AND SHEAR ON THE VISCOELASTIC PROPERTIES OF SOY FLOUR DOUGH

This paper is concerned with the effect of heat and shear on the rheological properties of defatted soy dispersions and doughs of 30 to 60% flour by weight. Capillary and rotary rheometers (Rheometrics Mechanical Spectrometer) were used to heat doughs up to 75° C and shear them simultaneously. In one series of experiments using a modified Instron capillary rheometer the doughs were heated to several different temperatures and then sheared. The linear viscoelastic properties of the dough which were determined by means of a plate-plate rheometer were then compared to the fresh dough and those of a heated but nonsheared dough. In another experiment a cone-and-plate rheometer was used to heat and shear the dough. The linear viscoelastic response of the dough was used to monitor any changes as it was heated and sheared. It was observed that only in the higher moisture dispersions (i.e., moisture contents greater than 50%) were there any signs of an increase in rheological properties which might be associated with “cooking”. It was concluded that cooking of soy flour doughs most likely does not involve the formation of a permanent network formed by covalent chemical bonds. Hence, in extrusion cooking processes involving soy flour doughs, it may not be necessary to treat the rheological properties of the dough as a thermosetting system.     

EFFECTS OF STARTER CULTURES ON LINEAR VISCOELASTIC AND PHYSICAL PROPERTIES OF YOGURT GELS

Set-style yogurts were produced from cow's milk under standard conditions by using 11 commercially available starter cultures. Samples were prepared in control beakers and within the Couette device of a dynamic rheometer. Repeatability of rheometer yogurt fermentations proved to be satisfactory. Within the linear viscoelastic region a significant inverse relationship between storage modulus and tan δ of yogurt samples was found. Specific properties of starter cultures clearly affected response in dynamic frequency sweeps and in stress relaxation experiments. Dynamic and relaxation data showed good agreement. Relaxation spectra H(τ) were obtained from dynamic measurements and stress relaxation by approximation methods. Both the shape of H-τ curves and the magnitude of H was affected by starter cultures. As compared to literature data on model casein gels and microstructural findings on yogurt the results imply that (a) a permanent network exists in yogurt, (b) interactions with long relaxation times contribute less to viscoelasticity in the case of yogurt produced with viscous starter cultures, and (c) attachment of mucogenic bacteria to the protein matrix via exogenic polysaccharides decreases yogurt firmness.     

INFLUENCE OF EGG YOLK LIPOPROTEINS ON THE RHEOLOGY AND STABILITY OF O/W EMULSIONS AND MAYONNAISE 1. VISCOELASTICITY OF GROUNDNUT OIL-IN-WATER EMULSIONS AND MAYONNAISE

Viscoelastic properties of groundnut oil-in-water emulsions stabilized by egg yolk and of mayonnaise have been deduced from their creep compliance-time response to a constant low shear stress. The viscoelastic parameter values, emulsion stability and initial mean drop size were influenced by pH and NaCl, due to disruption of the egg yolk components. When carboxymethylcellulose was incorporated in the continuous phase of the O/W emulsions an egg yolk-carboxymethylcellulose complex was formed and this affected the rheological properties of the emulsions and also their stability. Mayonnaises exhibited more pronounced viscoelasticity and greater stability than the O/W emulsions. At elevated temperature the micelles adsorbed around oil drops degrade. Their lipoprotein structure unfolds so that more segments on adjacent drops are then available for interlinking and network formation.     

EFFECT OF METHOCEL AS A WATER BINDER ON THE LINEAR VISCOELASTIC PROPERTIES OF MOZZARELLA CHEESE DURING EARLY STAGES OF MATURATION

Changes in the dynamic and transient rheological character of highmoisture, skim milk (HMSM) Mozzarella cheese due to the addition of 0.2% Methocel (methyl cellulose) as a water binder at room (25C) and refrigeration (7C) temperatures during early stages of maturation (1, 5, 7, and 14 days after manufacture) were investigated. The HMSM Mozzarella with 0.2% Methocel was softer (lower dynamic storage and loss modulus, and higher creep and recovery compliance) compared to HMSM Mozzarella without Methocel, due to improved water holding capacity. The age-dependent frequency dispersions of dynamic mechanical spectra (storage and loss modulus) were fitted to a power-law model. A six-element Voigt-Kelvin mechanistic model described the age-dependent retardation spectra (compliances, viscosities, and retardation times) obtained from creep experiments. Strong correlation was obtained between the viscoelastic     

温度对南美白对虾肌原纤维蛋白质性质的影响

南美白对虾是当今世界养殖虾类产量最高的三大品种之一,因此研究虾的保鲜具有重要意义.以肌原纤维蛋白质的变化为依据,反映南美白对虾的鲜度和加工特性,考查不同温度对南美白对虾蛋白质性质的影响.结果表明在40℃时,肌原纤维Ca-ATPase的失活速度与溶解度下降速度接近,肌原纤维蛋白在较短的时间内发生变性;30℃时溶解度的下降比Ca-ATPase的失活速度快.在以上两个温度下,Ca-ATPaae的失活速度均遵循一级反应定律;低温下(0℃,4℃)Ca-ATPase的变化与溶解度的变化差别不明显,表明肌原纤维蛋白质的变性速度明显减慢.     

THE EFFECT OF INCREASED STEEPING TEMPERATURE ON MALT PROPERTIES

Steeping barley at 30°C instead of 16°C can reduce malting time by 24 hours. The malts produced have normal analytical values but the mashes filter slowly and the malts would be expected to give poor wort separation in a brewery. These run-off problems probably result mainly from starch-protein interactions.     

EFFECT OF SOAKING TIME AND TEMPERATURE ON TEXTURAL PROPERTIES OF SOYBEAN

Dry soybean seeds were soaked in water for 15 to 300 min at temperatures of 50C, 60C, 70C, 80C and then compressed 75% two times with an Instron in a texture profile analysis type of test. A multiple regression analysis showed a nonlinear function of time and temperature of hydration for all the three textural parameters and can be used for determining the blanching conditions for obtaining any desirable texture of the product.     

THE INFLUENCE OF WORK SOFTENING ON THE VISCOELASTIC PROPERTIES OF BUTTER AND MARGARINE

Abstract Creep compliance-time studies at low stresses give more information about the structural changes in work softened butter and margarine than the Cone Penetrometer. They show that margarine undergoes a greater structural change than butter. Margarine loses most of its instantaneous elasticity in an unrecoverable manner. However, most of the Newtonian viscosity loss is recovered. Butter loses much less of its instantaneous elasticity, and most of what is lost is recovered during aging, but less of the Newtonian viscosity which is lost is recovered. Retardation spectra derived from creep compliance-time curves for both butter and margarine before work softening show a peak at ∼10⁴ sec. In contrast to margarine, butter does not lose this peak when work-softened. For margarine, the peak slowly redevelops during aging and occurs at ∼10² sec. Past interpretation of Cone Penetrometer data has been based on the simplified concept of primary irreversible bonds and secondary reversible bonds, and the changes in their relative proportions during work softening. The present approach avoids the allocation of bond strengths into these arbitrary categories, and is based on the realization that butter and margarine contain a wide range of bond strengths.     

EFFECTS OF TEMPERATURE AND MOISTURE CONTENT ON THE VISCOELASTIC BEHAVIOR OF COWPEAS

The viscoelastic parameters of cowpeas (Vigna unguiculata) were studied at different temperature and moisture content combinations. Cowpeas were tested at temperatures of 25°, 45° and 70°C and moisture contents of 13.9, 19.6 and 22.4% dry basis on an Instron Universal Testing Machine using stress relaxation techniques. The response of cowpeas was characterized by two Maxwell bodies in parallel without the incorporation of a residual spring. The relaxation curves (uniaxial modulus versus time) were used to calculate temperature and moisture shift factors, which subsequently led to the construction of a single master response curve. Cowpeas are both thermo-rheologically and hydro-rheologically simple biological materials.     

THE EFFECT OF TEMPERATURE ON SOME RHEOLOGICAL PROPERTIES OF WHEAT FLOUR DOUGHS

Abstract. Doughs from three flours were sheared between a cone and plate at constant rates in the range 6 times 10^-4-2 times 10^-2 s^-1.
At temperatures between 25 and 40C, the apparent viscosity decreased with increasing temperature and with increasing rate of shear. The effects of the temperature and of the rate of shear were independent one of another, and can be described by an Arrhenius type equation and a power equation, respectively. At temperatures between 45 and 60C, the apparent viscosity increased rapidly with increasing temperature; this is ascribed to starch gelatinization. In this temperature range, the apparent viscosity decreased more rapidly with increasing rate of shear than at lower temperatures.
At temperatures between 25 and 45C, the shear modulus decreased with increasing temperature and slightly increased with increasing rate of shear. From the former fact it is concluded that the elasticity of dough has an origin different from rubber elasticity. In this temperature range, the shear modulus can be described by an equation similar to that for the apparent viscosity. At temperatures between 45 and 65C, the modulus increased with increasing temperature, though to a lesser extent than the apparent viscosity.
Changes in the rate of stress relaxation are in accordance with the effects of temperature and rate of shear on the apparent viscosity and the modulus.     

EFFECT OF TEMPERATURE CYCLING ON THE CRYSTALLINE FORM, SIZE AND TEXTURAL PROPERTIES OF SHORTENING FATS

Temperature cycling significantly reduced the solid fat content, peak force and firmness. The fats with the highest level of palmitic acid were the most stable in the β' polymorphic form. Those with the lower palmitic acid content changed to the β polymorphic form on isothermal storage as well as temperature cycling. In spite of these polymorphic changes, no dramatic change in other physical characteristics occurred.